micropenis An abnormally small penis. In medical practice, the dimension of the penis that is measured is the length. The measurement is taken along the upper surface of the shaft of the penis to the tip, using a measuring tape or, preferably, a ruler. The ruler is pressed firmly into the soft tissue over the…
microorchidism Abnormally small testes. To determine if the testes are too small, a device called an orchidometer is used that permits a testis to be compared to a series of plastic ovals (like miniature American footballs) of differing sizes. Microorchidism is a diagnostic feature, for example, of Prader-Willi syndrome and certain other multiple malformation syndromes….
microhematuria See blood in the urine.
microdeletion Loss of a tiny piece—a piece that may be too small to be seen readily through a microscope—from a chromosome. Microdeletions can be detected via high-resolution chromosome banding, molecular chromosome analysis (with FISH), or DNA analysis. Disorders caused by microdeletions include Angelman, DiGeorge, Prader-Willi, and Williams syndromes.
microcytic Literally, referring to any abnormally small cell; in practice, referring to an abnormally small red blood cell. For example, microcytic anemia is characterized by small red blood cells. The opposite of microcytic is macrocytic.
microcystic corneal dystrophy See Cogan corneal dystrophy.
microcephaly An abnormally small head due to failure of brain growth. Microcephaly is an ominous sign because it is almost always associated with developmental delay and mental retardation. Many factors can impair the growth of the brain, including intrauterine infections (such as rubella, cytomegalovirus, and toxoplasmosis), intrauterine chemical exposure (such as in fetal alcohol syndrome),…
microbe A minute organism typically visible under a microscope. Microbes include bacteria, fungi, and protozoan parasites.
microangiopathy A disease of the capillaries (very small blood vessels), in which the capillary walls become so thick and weak that they bleed, leak protein, and slow the flow of blood. For example, diabetes predisposes to the development of microangiopathy in many areas, including the eye.
micro- Prefix meaning small, as in microcephaly (small head) and microsomia (small body). The opposite of micro- is macro-.
MI Myocardial infarction. See heart attack.
MHC Major histocompatability complex.